The 18-year-old Karl has been sensational for Bundesliga leaders Bayern this season while teammate Urbig has stepped in as Bayern's starting goalkeeper following veteran Manuel Neuer's injury.
With Oliver Baumann seen as Germany's first-choice keeper, Urbig is likely to serve as a reserve for the World Cup, with Marc-Andre ter Stegen struggling to regain full fitness and Neuer having retired from international football.
"(Karl) won't get too much pressure from me. I just want him to do what he does at Bayern. Bring what a young player can bring into the game," Nagelsmann told a press conference on Thursday. Germany will travel to Switzerland on March 27 before hosting Ghana three days later.
Nagelsmann cautioned that while the current squad could be very similar to the World Cup squad to be announced in May, changes were still likely.
"The March squad has many parallels to the squad in May but this is not yet a World Cup squad nomination," the coach said.
Nagelsmann rested some experienced players, including playmaker Jamal Musiala, who is nursing a minor injury to the ankle he broke last year.
"He has some pain but that is normal after such an injury. We are interested in him being firstly fit for Bayern, to play many games so that he can be considered. Under the circumstances... we will give him the necessary time to recover."
Nagelsmann also recalled forward Deniz Undav, the Bundesliga's leading German scorer with 16 goals, as well as Kai Havertz, Anton Stach, Pascal Gross and Antonio Rudiger among others.
Germany have set their sights on winning the World Cup following shock group-stage exits in 2018 and 2022, determined to restore their reputation as a global football powerhouse. The tournament starts in June and is co-hosted by Mexico, the United States and Canada.
The Germans, who have not reached a final in any major international tournament since winning their fourth World Cup in 2014 in Brazil, have been drawn in Group E with Ecuador, Curacao and Ivory Coast for the tournament that runs from June 11 to July 19.
They play their opening World Cup match in Houston, Texas on June 14 against Curacao. The Germans then travel to Toronto on June 20 to take on Ivory Coast before their last group game against Ecuador in New York on June 25.